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I have a 3-way light switch that I just replaced with a new illuminated one (glows when off). The light inside the switch is pulsating, like a heartbeat! I thought it was maybe a defective switch and changed it again with another new illuminated one, but still the same flickering. So it's definitely not the switch. What else would it be?

Additional context, this is part of a 4-way circuit in my hallway, including two 3-way switches and one 4-way switch. The lights turn on/off correctly, despite the flickering illuminated switch. And it's just one switch. I didn't change any of the wiring or terminal connections - just swapped old light switches for new ones.

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    Could you share a photo of the switch or its model number? In times past switches were illuminated with neon lamps which naturally have a characteristic flicker. LED illumination is a thing now, but I wonder whether the switch you chose uses neon.
    – Greg Hill
    Dec 4 '20 at 21:28
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    What model of switch? Are the lamps incandescent? Pulsating may mean a switch designed for incandescent lamps where ballasts or drivers used with CFL’s or LED’s don’t have the leakage path that an incandescent lamp has this would be my guess with the info provided.
    – Ed Beal
    Dec 4 '20 at 21:33
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What model of switch? Are the lamps incandescent? My answer with the info provided: Pulsating may mean a switch designed for incandescent lamps where ballasts or drivers used with CFL’s or LED’s. These lights don’t have the leakage path that an incandescent lamp has. this would be my guess with the info provided. In some cases older LED’s the switch lamp can cause your lights themselves to strobe like a heartbeat. Look up strobing LED and you will probably find similar issues like you have.

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    Thanks for the answer. I was not the person who asked the question, but I had a similar issue. It did turn out to be the fluorescent light. Either removing the fluorescent light or adding an LED light solved the problem. I am guessing there needed to be something on the line with a leakage path. Jun 1 at 22:13
  • @scott m stolz thanks for responding with a comment that this answer was helpful!!! this is what this site is all about. We hope to help others as this answer helped you, even if the original person never accepted a answer. Thank you for letting us know the information was helpful,,, Ed Beal.
    – Ed Beal
    Jun 2 at 4:39
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In my case, it was because the light switch serviced a linear fluorescent lamp (a shop light in the garage). A CFL is a compact fluorescent lamp, so it may have the same issues. So it might be the type of bulb you have installed.

In my case, the switch turned on and off an outlet and the light was plugged into the outlet. This made it easy to test.

Test Results:

  1. Fluorescent lamp only = pulsing illuminated switch.
  2. LED lamp only = illuminated switch worked normally, no pulsating.
  3. LED Lamp and Fluorescent both plugged in = illuminated switch worked normally, no pulsating.

This might have to do with the "leakage path" that Ed Beal mentioned in his answer. I am assuming the LED had one, and the fluorescent did not. Either way, the pulsing stopped once I added the LED lamp to the circuit.

Try different bulbs and see if that is the cause.

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